1. Field of the Invention
The present invention relates to an electronic apparatus having a battery as an electrical power source, and more particularly to a comparatively small electronic apparatus such as a calculator, a pocket radio receiver, a tape recorder, a tester or a video camera.
2. Description of the Prior Art
In an electronic apparatus such as described above, as an electrical power consumption in calculation and other electronic circuits has decreased, a density of central processing units has increased, and a mounting density of printed circuit boards, LSIs, ICs and other electronic components or devices has increased, disadvantages such as malfunctions and destruction of central processing units due to static electricity and radio wave noise from external sources have occurred. Furthermore, there has been a concern that noise generated by a motor disposed inside the electronic apparatus may cause malfunctions in the electronic circuits and that radio waves generated by an oscillator which is one of the electronic circuits in the apparatus may become a noise source to other electronic apparatus such as a radio receiver.
A grounded conductive member which has a wide surface area and is mounted to an apparatus as a noise shield plate is an example of means for eliminating these defects.
FIG. 1 shows an outer appearance of a calculator with a printer having recording functions as an example of this type of small electronic apparatus.
In FIG. 1, reference numeral 1 denotes an outer case of the apparatus. The outer case 1 has a lower case lA and an upper case 1B which are engaged with each other or abutted on each other. These half cases lA and 1B are secured to each other to form a single structure by a screw or similar member.
In an inner space in a front portion of the outer case 1, formed is a housing portion for an electronic calculation circuit and a battery as an electrical power source. An inner space in a rear portion of the outer case 1 houses a printer mechanism of a suitable system. A recording paper is housed in a rear portion of the printer mechanism. A cover 4 is disposed so as to cover the recording paper.
A keyboard portion 2 for inputting numerical data and operators is disposed on the surface of the front half portion of the upper case 1B. Moreover, a display device 3 for displaying input data and the results of calculations is disposed in a boundary portion between the front portion and the rear portion of the upper case 1B.
Next, an explanation will be made of the arrangement in the vicinity of the battery housing portion disposed in the inner space of the front portion of the outer case 1 of the apparatus with reference to FIGS. 2 and 3.
FIG. 2 is a cross-sectional view, and FIG. 3 is a perspective view showing a disassembled arrangement corresponding to FIG. 2.
As shown in FIG. 2, in an apparatus having a primary battery as an electrical power source, the predetermined number of batteries 6 are housed in a housing portion 5 recessed in the lower case 1A in order to facilitate to replace these batteries An electrode 6A of the battery 6 contacts a connecting member 7 disposed in the housing portion 5 so as to supply electrical power.
In order to electrically connect a printed circuit board 8 on which electronic circuits are disposed to the connecting member 7, generally used is a method of connecting the connecting member 7 to a predetermined pattern on the printed circuit board 8 via a lead wire or the like. Alternatively, as shown in FIG. 2, the connecting member 7 is directly soldered to the printed circuit board 8 with a solder 9 so as to reduce the number of assembly steps.
Further, reference numeral 10 denotes a lid mounted detachably to the battery housing portion 5 so that it can be opened and closed when replacing the battery 6.
The keyboard portion 2 for inputting numerical data and operators, which is formed on the top of the upper case 1B, has key buttons. On the upper surface of the key buttons, the content or function of an input such as numbers and symbols are indicated. Each key button 11 which is movable upward and downward with respect to the upper case 1B is positioned by a key rubber 12 formed from a resilient member in a condition so that the key button 11 is always biased upward.
A movable contact 13 made from a conductive material is integrally formed on the lower surface of the key rubber 12 by printing or molding. When the movable contact 13 contacts a corresponding key pattern disposed on a key printed circuit board 14, a key input signal is generated.
Reference numeral 15 denotes a reinforcement plate mounted on the lower surface of the key printed circuit board 14 so as to reinforce the key printed circuit board 14. The reinforcement plate 15 is formed from a metal material in the form of thin sheet having adequate strength. The key rubber 12, key printed circuit board 14 and the reinforcement plate 15 are securely attached to the upper case 1B.
In this calculator with printer which is an example of the prior art, the reinforcement plate 15 that is made from a metal member is connected to a grounding line, and is used as a noise shield plate to increase resistance to noise and resistance to static electricity.
As shown in FIG. 3, a lead wire 17 is soldered to a portion of a grounding pattern 16 formed on the printed circuit board 8. A lug terminal 18 is attached to an end of this lead wire 17, and this lug terminal 18 is tightly attached by a screw 20 to an attaching hole 19 formed in the reinforcement plate 15 so that the reinforcement plate 15 is electrically connected to the grounding line.
Reference numeral 7B in FIG. 3 denotes a connecting member contacting a negative electrode of the battery 6. Reference numerals 5A and 5B denote openings for inserting connecting members 7 and 7B respectively into the battery housing portion 5.
The above arrangement involves, however, the additional operations of soldering the lead wire 17 and of tightening the lug terminal 18 on the reinforcement plate 15 by the screw 20, thereby increasing the number of assembly steps and the costs of components. Additionally, defects that the lead wire 17 may be caught between the outer cases 1A and 1B when engaging the lower case 1A with the upper case 1B, and that the lead wire 17 may be broken erroneously during assembly because the reinforcement plate 15 and the printed circuit board 8 are always connected by this thin lead wire 17.